1. Field of the Invention
This invention relates to an autofocus apparatus for performing automatic focusing in a camera.
2. Description of Related Art
In conventional photographic cameras having autofocus apparatus, automatic focusing has been performed by detecting the amount and direction of deviation, along the optical axis, of the image plane where an object image is formed by a taking lens from the film plane, and moving the focusing optical system of the taking lens in accordance with the detected defocus amount and direction.
In such cameras, the drive amount of the focusing optical system is obtained by the formula: drive amount=movement coefficient.times.defocus amount and direction, using the movement coefficient inherent to each taking lens.
The movement coefficient inherent to each taking lens is stored in a non-volatile memory means for each taking lens and read out when it is needed.
On the other hand, in the case of such lenses as zoom lenses and macro lenses, a proper automatic focusing cannot be performed by using the same movement coefficient for their whole range of movement. In such a case, a plurality of movement coefficients are stored in the memory means, the position of the zoom lens or the focusing optical system is detected by a zoom encoder or a distance encoder, and a movement coefficient in the memory means corresponding to the detected positional information is used to make a proper automatic focusing.
Thus, the conventional autofocus apparatus requires the movement coefficients inherent to taking lenses or to the states of taking lenses and therefore need a plurality of memory means for the respective taking lenses, and a zoom encoder or an distance encoder, if necessary. Hence, the structure of the apparatus is much complicated.
Further, the movement coefficients inherent to the taking lenses are set in accordance with their design values, and the actual values may be different from the design values due to manufacturing errors. This results in an improper automatic focusing.